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Chicago birders are enjoying an amazing winter. You may have read about the ivory gull that showed up first at Montrose Harbor and then at Burnham Harbor. The ivory gull is a bird of the high arctic. It nests on the northern coast of Greenland and on various barren arctic islands.

In winter it lives at sea, scavenging the remains of polar-bear kills on the ice floes. Northern hunters used to lure the bird by spilling seal blood on floating ice.

The ivory gull usually moves only as far south as the edge of the ice pack. The only previous Chicago-area record for the species is a rather poorly documented--but probably accurate--sighting near Waukegan in 1949. This winter's bird was quite cooperative, not only showing up on a daily basis at Burnham Harbor, but also showing up over the New Year's holiday so lots of people could come see it without having to take time off work.

The ivory gull is only one of the notable arctic visitors the midwest has enjoyed this winter. A Ross's gull sighted near Saint Louis has drawn birders from all over. Ross's gulls were almost never seen in the lower 48 until recent years. They are circumpolar in distribution, and some people theorize that they have established nesting grounds at the mouth of Hudson Bay that are the source of the birds reported in the lower 48 in the past decade. The Saint Louis bird may have moved on. The Chicago Audubon Society's rare-bird hotline (708-671-1522) reported last Thursday that the Army Corps of Engineers had flooded the area where the bird had been hanging out, and that it was no longer being seen.

But Chicago has a lot besides the ivory gull to get excited about. Last Sunday a bird that was probably an immature mew gull was reported from Montrose Harbor. The people who saw it are experienced birders, but this is a very difficult call. The mew gull lives in Eurasia and on the Pacific coast of North America. It has been seen only three times before in Illinois, and none of those sightings was in the Chicago area. Immature mew gulls sport plumage that looks very much like the plumage of immature ring-billed gulls, and ring-billed gulls are our most common local species. You have to separate the two species on the basis of factors such as size and bill color. The birders who reported the species took some pictures, which may resolve the question, but more sightings by birders with enough experience to be able to tell a mew gull from a ring-billed would be helpful.

If this bird was indeed a mew gull, it could have come from the west, but it is more likely that it came from Europe. In recent winters there have been reports of sightings in New England and the Canadian Maritime Provinces. It would be fairly easy for a water bird to follow the Saint Lawrence River and the Great Lakes to locations far from the sea. The fact that two mew gulls have been reported from the Milwaukee lakefront would seem to add credence to the Montrose sighting.

An ivory gull and a mew gull are spectacular sightings for this region, but they are by no means the only rarities around. Consider, for example, the Kittlitz's murrelet sighted off the Northwestern University landfill.

Friedrich Heinrich Kittlitz was a German soldier and naturalist who was part of an 1826 Russian expedition that visited Kamchatka, the Siberian peninsula that separates the Sea of Okhotsk from the Bering Sea. Brachyramphus brevirostris was given its English name in his honor.

Murrelets are small members of the family Alcidae, the group of northern seabirds that also includes murres, puffins, auks, and auklets. They are approximate ecological equivalents of the penguins of the southern oceans, but differ from the antarctic birds most obviously in their ability to fly. There was one flightless alcid, the giant auk, but it was last seen alive in 1841. Actually the giant auk was the original penguin; Welsh sailors combined the Welsh words pen (head) and gwyn (white) to designate the bird, which had a large white patch on each side of its head.

However, I digress. Kittlitz's murrelet lives along the shores of the Bering Sea and the north Pacific on both the Alaskan and Siberian coasts. Its center of abundance in North America is in the vicinity of Glacier Bay near Juneau. It nests in the mountains above the timberline, often many miles from the sea. No one has ever seen one in Illinois before, but a bird was seen in Lake Michigan off Michigan City, Indiana, in 1983. This year's murrelet put in a brief appearance a couple of weeks ago and has not been seen since.

Meanwhile, what might be described as the regular rarities of winter are showing up all over the place. We have snowy owls up and down the lakefront. Meigs Field seems to be very attractive to these tundra owls. One can usually be found there every winter, but this year we have several others at various lakefront locations from Chicago to Waukegan. I saw one sitting on a light pole at Montrose during the Thanksgiving holiday.

The regular but rare winter gulls are also somewhat more common this year. The lesser black-backed gull seems to be continuing its penetration of North America. This bird was never seen in the Chicago area before 1962, when an adult showed up at Willow Slough in Indiana, and it was another 20 years before the second sighting. Lately it has been a winter regular. This is a Eurasian species, but it has also become regular along the east coast in recent years.

We also have numerous sightings of glaucous, greater black-backed, and Iceland gulls, the more usual gulls of our winters.

Down at Indiana Harbor birders have found both a western grebe and a red-necked grebe. Both of these species are considered rare migrants in fall and practically unheard-of in January.

Our greenhouse winter seems to be causing lots of migrants to linger well past their usual time. Canada geese have inflicted serious disappointment on hunters in southern Illinois by staying north to enjoy the balmy weather. And bobbing in the waves just off Calvary Cemetery at the south end of Evanston is an enormous raft of diving ducks that includes both surf and black scoters and about 3,500 scaup.

We have two species of ducks called scaup, the greater scaup and the lesser scaup. They are difficult--but possible--to tell apart in the field. Most of them pass through here in the fall on their way to Chesapeake Bay and other coastal waters of the Atlantic and the Gulf of Mexico where they spend the winter.

Both scaup eat a mix of vegetable and animal foods. Lesser scaup tend to feed in water up to about six feet deep, while greater scaup dive as deep as 20 feet after food. However, both birds are flexible, and lesser scaup sometimes feed in deeper water and greater scaup in the shallows. They take some small fish, but most of their animal food is either slow moving or stationary. They like oysters, snails, clams, mussels, and other mollusks.

In an average winter Lake Michigan would be inhospitable for these birds because the shallow near-shore waters freeze. The only open water would be too deep for them to feed in. Our warm winter has left the lake completely ice free, so lots of food is available. Why risk a flight to Maryland or Louisiana when things are good right here?

There is another possible contributing factor here, and that is our old friend the zebra mussel. We have been hearing a lot about what a menace this alien shellfish is as it spreads through the Great Lakes, and it is true that the problems it is creating are serious and often expensive to deal with. And I would not want to say anything that might encourage people to think that allowing alien species into an ecosystem is no big deal. But the fact is, diving ducks will eat zebra mussels. There are reports of increases in winter duck populations on Lake Erie, increases thought to be caused by the availability of a new food source, the zebra mussel. I don't think we have enough zebra mussels at this end of Lake Michigan--yet--to support 3,500 scaup for very long, but the pesky mollusks could make a continuing difference in the ability of the lakes to support winter populations of diving ducks.

All of which points to the complexity of even battered and depauperate ecosystems like those of the Great Lakes. A new species can have powerful effects, both good and bad, and it may take a century or more to sort everything out.

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